(1) Field of the Invention
The present invention relates to a data stream selection/output apparatus that selects a data stream out of a plurality of data streams each of which is composed of sequentially obtained data and outputs the selected data stream.
(2) Description of the Related Art
In the terrestrial television broadcasting, a program distribution system has been established. In the system, a key station distributes TV programs to a plurality of local stations, and each local station broadcasts the distributed broadcast programs according to their broadcasting schedules as well as other self-made broadcast programs and commercials. In the broadcasting, the local stations use a device called switcher. The switcher is a data stream selection/output apparatus that stops outputting a data stream of moving pictures, voices or the like and starts outputting another data stream, based on a broadcasting schedule.
Meanwhile, when a switcher selects and outputs a compressed data stream (for example, a transport stream (abbreviated as TS) conforming to the MPEG2-TS (Moving Picture Experts Group 2-Transport Stream) defined in the ISO/IEC13818), there are some matters to be taken care.
For example, when a switcher selects and outputs an elementary stream (abbreviated as ES) containing compressed image data conforming to MPEG2, a care should be taken so as not to partition the units of GOPs (Group Of Pictures). This is because such incomplete GOPs would cause a failure in the bidirectional prediction which is performed when compressed image data is decompressed. This causes irregularity in the reproduced and displayed images.
Japanese Laid-Open Patent Application No. 2001-517040, aiming to solve the above-described problem, discloses a technique in which a plurality of compressed programs are spliced together to be seamless.
The above-introduced document, however, does not disclose or suggest a matter to be dealt with when a switcher selects and outputs an elementary stream in the data broadcasting. Note that the data broadcasting is a form of digital broadcasting in which, for example, elementary streams conforming to the DSM-CC (Digital Storage Media Command and Control) protocol defined in the ISO/IEC13818-6 are broadcast. The DSM-CC protocol extends over Session Layer and Application Layer which are higher than Transport Layer in the OSI Reference Model. An elementary stream conforming to the DSM-CC protocol is composed of variable-length data blocks that are repeatedly transmitted in cycles, each data block no larger than 4 KB.
Here, if a conventional switcher, which supports only Transport Layer in the OSI Reference Model, is used to select and output an elementary stream for the data broadcasting, the broadcast elementary stream may include an incomplete section since it may partition the elementary stream in the middle of a section. If an elementary stream including such an incomplete section is broadcast, a receiving apparatus of the broadcast would recognize an MPEG standard violation and discard the section since a CRC value attached to the end of the section does not match a result of the calculation performed for the Cyclic Redundancy Checking.